Diagnostic test systems commonly employ indicator stripes or zones that change color or provide another visual indication of a test result. Rapid diagnostic test kits, for example, have been developed to detect and indicate the presence of a specific environmentally or biologically relevant species such as a hormone, a drug, a metabolite, a toxin, or a pathogen-derived antigen in a sample. In a common configuration, the sample, which may contain a target species, is applied to a test strip. The sample then flows along the test strip (e.g., through wicking) to indicator zones, where the presence of the target species in detectable quantities causes a change in the optical properties of the indicator.
Several mechanisms for causing detectable changes in the indictors are known. A binding assay, for example, typically uses a labeling substance and a capture zone that acts as an indicator. With a binding assay, the labeling substance binds to any of the target species present in the sample thereby forming a complex. Complexes that may have been formed in the test strip then flow to and are captured in the capture zone, where the labeling substance changes the capture zone in a detectable manner. For example, the labeling substance may contain a substance such as a reflective material, a dye, a fluorescent material, or a quantum dot that collects in the capture zone and produces a visible indicator for the target substance. The presence or absence of a measurable amount of the target species is thus indicated by the presence or absence of visible change in the capture zone.
Some test systems, such as drug test kits for employee screening, may test for multiple target species (e.g., multiple drugs or drug metabolites) and have multiple indicators respectively for the multiple target species. In general, test result evaluation for a multi-indictor test system has required human observation, an expensive detector system that separately measures the indicators, or an imaging system with pattern recognition. Means to distinguish among multiple indicators often depend upon optical differences of the indicators, e.g., fluorescent material of different wavelengths, or different temporal responses to optical stimulation. These bring the expense and complexity of multiple labeling and binding substances, multiple optical sources of stimulation and high speed circuitry. Means to distinguish among different indicator locations often depend upon movement of the test strip or scanning with either a light source or a sensor. These also bring the expense and complexity associated with motion or scanning control. Simpler or lower cost detection systems and methods that are capable of recognizing optical differences in multiple indicators and providing electronic output are thus sought.